Tire pressuring monitoring (TPM) devices are used in today's vehicles. A tire pressure sensor senses the tire pressure reading (or other conditions, such as the temperature of the tire). These sensed readings may be communicated to a TPM receiver that is disposed in the vehicle. A display screen may also be coupled to the receiver. When the tire pressure reading falls below a particular threshold, the driver of the vehicle may be alerted, for example, by an alert message being displayed to the driver on the screen. The driver can then take any required action.
Most TPM sensors have a specific frequency deviation when they transmit frequency-shift keying (FSK) data. For example, the frequency deviation may be 315 Mhz +/−20 hz or 40 khz of deviation (or range). Thus, 314.98 Mhz may be used for transmission of a logic “0” (in the FSK scheme) while 315.02 Mhz may represent a logic 1. The exact frequency deviation is chosen when the TPM sensor is engineered and must be in accordance with the bandwidth and frequency discrimination of the receiver used to receive the FSK data.
Many TPM sensors have a FSK frequency deviation of between +/−30 Khz to +/−50 Khz. This means that the bandwidth of the receiver must be around 200 kHz. A wide receiver bandwidth is cost effective, but is linked to more in-band noise coming from different sources. This in-band noise decreases the sensitivity of the sensor in some cases.
Some original equipment manufacturers (OEMs) require a smaller bandwidth receiver. Thus, the TPM sensor working with such a receiver must also limit its frequency deviation. In some cases, a TPM sensor with a wide frequency deviation may not be received at all by a narrow band receiver or can be attenuated.
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